Question

Which statements are true for two oppositely charged, isolated parallel plates: C=capacitance, U=stored energy (Q and -Q = charge on the plates). Note: Isolated plates can not lose their charge.
1. Inserting a dielectric decreases U.

2. When the distance is doubled, C increases.

3. Increasing the distance increases the Electric field.

4. Inserting a dielectric increases Q.

5. Inserting a dielectric increases C.

6. When the distance is halved, Q stays the same.

7. When the distance is doubled, U increases.

Answer 1

Answer:

Explanation:

1) True. The stored energy (U) is proportional to the electric field strength (E). The electric field strength decreases when a dielectric is introduced hence inserting a dielectric decreases U.

2) False. From the formula $C=\frac{Q}{V}=\frac{Q}{Vd}$, capacitance is inversely proportional to distance hence if the distance is doubled, capacitance decreases.

3) False. As the distance between the electric field and the object increases, its electric field decreases.

4) False. If a dielectric is inserted, the plates are further separated. Q stays the same.

5) True. The electric field strength decreases when a dielectric is introduced and  capacitance is inversely proportional to electric field hence Inserting a dielectric increases C

6) True. If a dielectric is inserted, the plates are further separated. Q stays the same.

7) True. When the distance is doubled, U increases